The present invention relates generally to fluid surge protection in fluid distribution protection in an underground city water system of the type generally having a series of fire hydrants interconnected by water mains and outlets.
In a conventional underground city water system, fire hydrants are fed by an underground supply pipe and typically include underground shut-off valves in which some control the flow of water to each hydrant. Hydrants contain a manually operable valve which is operated by a fireman to release water from the underqround supply pipe in an event of fire or during training exercises. Also hydrants are opened by city workers or others in order to clear sedimentation from water mains. Typically, the hydrant valve is located underground. Except in tropical climates where the ground does not freeze, it is generally necessary to bury below the frost line all of the parts of the system which normally retain standing water or slow moving freezable liquids.
The hydrant valve is usually controlled by a stem extending vertically from the buried valve passing through the top of the hydrant. A shut-off auxiliary valve, which is separate from the hydrant valve, is usually provided with an access conduit extending vertically to a removable access cover located at ground level adjacent to the hydrant. The access cover is removed and a removable wrench, commonly known as a valve key, is inserted through the access conduit to operate the shut-off valve.
Water surge can be a severe problem in a distribution system. Water surge results when a valve at one point in a hydrant system is opened or shut suddenly, creating a pulse in the unbroken conduit of water upstream and downstream of that valve. In addition, when a pump or other source of pressurizing of the main is actuated additional flows are created or diminished. Since water is essentially incompressible, it does not absorb the energy of the pulse, but transmits it throughout the distribution system to nearby or distant parts of the system which are not isolated behind a closed valve. Water surge is capable of parting joints, breaking water mains and other components of the system. Since the system is mostly buried, time is sometimes required to pinpoint the damage area and then time is always required to correct the resulting damage. The water escaping from the damaged system can cause a pressure failure, a pavement collapse, and is moderate to very dangerous to repair. The danger occurs with trench cave-ins during working and with the possibility of breaking, or causing an explosion of a gas or other utility line.
In addition, the water surge caused by shutting the hydrant valve or by activating any inlet or outlet of the system has often damaged the nearby shut-off valve located at the same inlet or outlet. Furthermore, the shut-off valve body and the hydrant valve body (and sometimes intervening piping as well) are typically separate parts joined together. The joints intervening between these valves at a particular outlet sometimes part when a water surge is created by operating the hydrant valve too suddenly, especially whenever the hydrant is not properly blocked. Parting will occur in other liquid transmission systems by creation of perturbations in the liquid. Thus, the advantage exists to protect each shut-off valve against water surge originating at the adjacent hydrant valve.